1. Technical Field
This disclosure relates to a voltage converting controller, a voltage converting circuit, and a control method for voltage converting, and in particular, to a voltage converting controller, a voltage converting circuit, and a control method for voltage converting which can mitigate an overshoot and undershoot of an output voltage and may also have desirable power conversion efficiency when a heavy load and a light load frequently appear alternately.
2. Related Art
A switching voltage converting circuit is one of voltage converting circuits, and in a manner of switching a power switch, regulates energy stored on an inductive component (for example, a transformer) to supply the energy to an output load, and converts an input voltage into an output voltage at an output terminal, so as to maintain a fixed output voltage value and provide a load current needed by the output load. Its advantage is that conversion efficiency is high, and therefore unnecessary heat generation can be reduced, thereby lowering complexity of a heat dissipation design.
However, on many electronic application apparatuses, for example, on a mobile phone, a load current supplied by a voltage converting circuit often involves an application scenario in which a heavy load and a light load frequently appear alternately. This is because at present an electronic application apparatus has an increasingly high integration level and increasingly complex functions; however, on the other hand, a requirement for electrical endurance of a system becomes increasingly high. Therefore, many functional blocks in an electronic system often quickly start and perform a function when needed, and switch off its power supply to save power. Therefore, for a system design of an electronic apparatus, a test of frequently switching a heavy load/light load of a power supply unit is more and more important, and becomes an important index for evaluating performance of the power supply unit.
In further description, at present, in designs of many switching voltage converting circuits, a positive correlation relationship exists between an operation frequency and the magnitude of a load current of the switching voltage converting circuit; that is, when the load current increases, an operation current also increases, and when the load current decreases, an operation current of the switching voltage converting circuit also decreases. This is because when the load current decreases and the output voltage is maintained by using a voltage stabilizing capacitor at an output terminal, its power loss speed is low, and therefore a low operation frequency may be used without making the output voltage too low; meanwhile, a switching loss may be reduced, which helps to improve power conversion efficiency of the switching voltage converting circuit, that is, can improve endurance of a battery. However, when the operation frequency is low, and the load current instantaneously changes from a light load to a heavy load, electric charge needed by the load can be instantaneously supplied only by the voltage stabilizing capacitor at the output terminal, until a next operation frequency period starts. Therefore, the output voltage possibly causes a severe undershoot, and even causes abnormal work of a circuit.
Please refer to U.S. Pat. No. 8,259,472 (hereinafter referred to as Prior Art 472). Prior Art 472 discloses a switching voltage converting circuit, of which an operation frequency and the magnitude of a load current are positively correlated. A technical solution of Prior Art 472 further includes a minimum instantaneous frequency, and when the magnitude of the load current changes from a heavy load to a light load, the operation frequency also gradually decreases. However, in a process in which the operation frequency decreases, when a frequency of the operation frequency is already equal to the minimum instantaneous frequency, the switching voltage converting circuit disclosed by Prior Art 472 makes the frequency of the operation frequency fixed at the minimum instantaneous frequency for a certain period of time, during which, if the load current changes from a light load to a heavy load, an undershoot of an output voltage can be made not too severe because the frequency of the operation frequency is high enough. In summary, after the frequency of the operation frequency has been fixed at the minimum instantaneous frequency for a certain period of time, if a condition in which a load current changes from a light load to a heavy load does not occur, the operation frequency is no longer maintained at the minimum instantaneous frequency, and an original mechanism is restored to continue with being corresponding to a frequency change of the light load.
However, in Prior Art 472, when a heavy load and a light load frequently appear alternately, the frequency of the operation frequency is maintained above the minimum instantaneous frequency, resulting in a sacrifice of power conversion efficiency.